[PATCH] gdb/dwarf2read.c: Sanity check DW_AT_sibling values.

[Will Newton <will.newton@linaro.org>]

When reading objects with corrupt debug information it is possible that
the sibling chain can form a loop, which leads to an infinite loop and
memory exhaustion.

Avoid this situation by disregarding and DW_AT_sibling values that point
to a lower address than the current entry.

gdb/ChangeLog:

2013-11-01  Will Newton  <will.newton@linaro.org>

	PR gdb/12866
	* dwarf2read.c (skip_one_die): Sanity check DW_AT_sibling
	values.  (read_partial_die): Likewise.
---
 gdb/dwarf2read.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 3974d0b..d4dfd45 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -7016,7 +7016,14 @@ skip_one_die (const struct die_reader_specs *reader, const gdb_byte *info_ptr,
 	    complaint (&symfile_complaints,
 		       _("ignoring absolute DW_AT_sibling"));
 	  else
-	    return buffer + dwarf2_get_ref_die_offset (&attr).sect_off;
+	    {
+	      const gdb_byte *sibling_ptr = buffer + dwarf2_get_ref_die_offset (&attr).sect_off;
+	      if (sibling_ptr < info_ptr)
+		complaint (&symfile_complaints,
+			   _("DW_AT_sibling points backwards"));
+	      else
+		return buffer + dwarf2_get_ref_die_offset (&attr).sect_off;
+	    }
 	}

       /* If it isn't DW_AT_sibling, skip this attribute.  */
@@ -15134,7 +15141,14 @@ read_partial_die (const struct die_reader_specs *reader,
 	    complaint (&symfile_complaints,
 		       _("ignoring absolute DW_AT_sibling"));
 	  else
-	    part_die->sibling = buffer + dwarf2_get_ref_die_offset (&attr).sect_off;
+	    {
+	      const gdb_byte *sibling_ptr = buffer + dwarf2_get_ref_die_offset (&attr).sect_off;
+	      if (sibling_ptr < info_ptr)
+		complaint (&symfile_complaints,
+			   _("DW_AT_sibling points backwards"));
+	      else
+		part_die->sibling = sibling_ptr;
+	    }
 	  break;
         case DW_AT_byte_size:
           part_die->has_byte_size = 1;
-- 
1.8.1.4